It seems ironic that the title of the movie is “Identity Thief” when its co-stars have such a firm grasp on their well-established screen personae.

Melissa McCarthy is the brash wild card with an off-kilter sense of humor and an underlying, slightly dangerous streak. Jason Bateman is the initially bemused but increasingly frustrated straight man whose deadpan quips seem to be the only things that keep him sane.

These two opposites are stuck on a cross-country road trip together but no one’s really going anywhere; to borrow from that famous Dennis Green rant when he was still coaching the Arizona Cardinals, “They are who we thought they were.” Optimally, with a better script, that wouldn’t be such a bad thing. Instead, “Identity Thief” strands these two ordinarily enjoyable comics in the middle of nowhere with no help for miles. “Midnight Run,” it is not. It’s actually not even “Due Date,” which felt similarly strained.

It’s not just that director Seth Gordon (“Horrible Bosses”) and screenwriter Craig Mazin (the reheated “Hangover Part II”) confuse meanness for hilarity. There’s that, including a weirdly uncomfortable streak of homophobia and/or emasculation. The fact that Bateman’s character’s name, Sandy, also could belong to a woman becomes a joke that’s not funny even once — it’s just adolescent — yet it gets hammered into the ground again and again. But eventually and abruptly the film takes a sappy, sentimental turn that’s handled rather awkwardly. It comes from nowhere and hasn’t been earned.

More fundamentally, though, the premise is just massively flawed. Bateman’s mild-mannered accounts processor, Sandy Patterson, discovers that someone has stolen his identity and racked up thousands of dollars in charges when he tries to fill up his tank and has his card denied. They all come from the same place — Winter Park, Fla. — and they started weeks ago. But Sandy lives in Denver.

Isn’t this suspicious? In theory, wouldn’t Sandy’s credit card company alert him, like, immediately that so much money was being spent at one time? My credit card company calls me if it looks like I’ve bought too many hoodies and cargo pants for my kid at Old Navy.

Nevertheless, with a promising new job and his family’s security in jeopardy — Amanda Peet gets little to do as the supportive wife — Sandy schleps to Florida to track down the perpetrator and drag her back to Denver to face charges. This is just the first in a series of contrivances that keep the narrative chugging along, implausibly.

When he finds the con artist — whose real name is Diana, supposedly — she looks harmless enough and even a little pathetic in her tacky house crammed with blenders and microwaves and other ill-gotten gains. But Diana is actually quite resourceful, and a survivor. Still, their relationship, which begins with a brutal brawl, unconvincingly evolves into a supposedly genuine friendship as they drive back to Denver together with various and sundry thugs on their tail.

Bateman’s character is written as a milquetoast corporate drone but as an actor he’s too smart, and too much of a smart-aleck, to play someone weak. McCarthy, as always, just goes for it and is a fearless physical comedian but too often she’s hampered by lame, repetitive gags; her character’s habit of punching people in the throat isn’t terribly amusing the first time.

She does, however, enjoy a kinky interlude with Eric Stonestreet as the wealthy good ol’ boy she picks up at a bar. It’s the only segment that feels unpredictable and even a bit daring — now that’s the movie I’d much rather see.